An AM Radio build with antenna design models, BOM, and schematic.
This section describes the criteria and techniques used to determine an antenna design for the radio.
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Medium Wave (MV) AM Radio. Frequency Range: 525kHz - 1600kHz.
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Using an AM "Loopstick" antenna consisting of a 140mm x 10mm cylindrical ferrite rod and 0-200pF variable air-gap capacitor + fixed 56pF ceramic capacitor in parallel (C=256pF).
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10 "taps" in the coil using a 10-position rotary switch.
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9V operating voltage (used in amplifier).
Based on the design criteria above, here is the produced antenna design.
Determine the combinations of L and C that produce frequencies in the desired range. In this case, the MW AM spectrum.
This heatmap can be produced using the model scripts/LCplotter.py.
Calculator: https://goodcalculators.com/resonant-frequency-calculator/
Radio Finder: https://radio-locator.com/
The inductance range needed for the coil was 150 - 400uH. The coil needs to have taps to allow the user to tune their radio to a desired resonance frequency. Here. 10 positions are used to cover from 150 to 400uH, as evenly spaced as possible. This is shown in the new heatmap below.
The capacitor can be varied freely at each tap position to fine tune the resonance frequency
This heatmap can be produced using the model scripts/LCplotter.py.
Length:
Diameter: 10mm
Number of Turns:
A 56pF ceramic capacitor in parallel with a 250pF variable air-gap capacitor.
2 Stage AM Radio consisting of AM Loopstick antenna (Design Above), Stage 1 Demodulation Circuit, Stage 2 Amplification Circuit, and Output Connector to 3.5mm audio jack.
Materials used to make this project.
antenna, coil, and tuning capacitor
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140mm by 10mm (diameter) ferrite rod
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1 roll of Magnet Wire
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1 1N34 Germanium Diode
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Electrolytic Capacitor
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Ceramic Capacitors
NOTE: For this project, an 8 ohm impedance output was desired (to use with modern earbuds). To use a high Z crystal radio ear piece, an output stage is likely not needed.
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1 audio jack
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1 audio amplifier chip
Just for decorative purposes
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Balsa wood
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Natural Wood Stain
http://techlib.com/electronics/crystal.html http://radio-timetraveller.blogspot.com/2011/01/unassuming-antenna-ferrite-loopstick.html https://radio-locator.com/ https://goodcalculators.com/resonant-frequency-calculator/ https://www.petervis.com/Radios/ferrite-rod-antenna-coil/calculator-for-mw-radio-coil.html https://coil32.net/online-calculators/ferrite-rod-calculator.html